Binding agents like monoclonal antibodies are useful in diagnosis and treatment of diseases like cancer. In canines (dogs), for example, a type of cancer is B cell lymphoma in which uncontrolled B cell proliferation can lead to illness and death. Lymphoma also occurs in humans and may be treated with anti-human CD20 antibodies, like Rituximab, for example. These antibodies, that react with or bind human CD20, generally do not bind canine CD20 (Jubala et al., Vet Pathol., July; 42(4):468-76, 2005; Impellizeri et al., Vet J., May; 171(3):556-8, 2006; Gravanis et al., The Oncologist, December; 15:1335-1343, 2010). Accordingly, binding agents capable of interacting with CD20 on the surface of canine B cells are desired. The technology described herein provides these reagents and therapeutics, as shown below.